Known is a tire pressure monitoring system which measures air pressure of tire interior spaces which are defined by a plurality of tires and a plurality of wheels provided at a vehicle, and enables to monitor whether the air pressure is normal or not. The tire pressure monitoring system disclosed in JP 2004-268612A includes a plurality of tire-based transmitting and receiving devices and a vehicle body-based transmitting and receiving device provided at the vehicle body side of the vehicle. The tire-based transmitting and receiving device is installed on each tire interior space and has an air pressure measurement means for measuring the air pressure of the tire interior space. In the tire pressure monitoring system disclosed in JP 2004-268612A, the vehicle body-based transmitting and receiving device wirelessly transmits the transmission request for identification information unique to each tire-based transmitting and receiving device and the measurement information measured by the air pressure measurement means to the tire-based transmitting and receiving devices. Then, the tire-based transmitting and receiving device receives the transmission request and wirelessly transmits its identification information and the measurement information. The vehicle body-based transmitting and receiving device is provided with transmitting antennas individually installed for each tire and the transmitting antenna is used for transmitting the transmission request. The vehicle body-based transmitting and receiving device transmits the transmission request to the tire-based transmitting and receiving device of each tire by turns. Namely, the vehicle body-based transmitting and receiving device is designed to determine which position the tire-based transmitting and receiving device, which sends back the identification information and the measurement information, is provided at the vehicle by transmitting the transmission request to the tire-based transmitting and receiving device after identifying the position of the tire.
In the tire pressure monitoring system disclosed in JP 2004-268612, in order to identify the position of the tire-based transmitting and receiving device, it is necessary to identify the position of a tire and then transmit the transmission request only to a tire-based transmitting and receiving device located at the tire. Thus, a transmitting antenna, which is used for transmitting the transmission request from the vehicle body-based transmitting and receiving device, is needed to be individually installed for each of tire-based transmitting and receiving device. Further, in order that the vehicle body-based transmitting and receiving device may receive the measurement information from all of the tire-based transmitting and receiving devices provided at the vehicle while being able to identify the position, the same number of transmission request as the number of the tire-based transmitting and receiving device must be transmitted by each transmitting antenna. Thus, processing load is increased in request transmitting processing for the transmission request and information receiving processing for the identification information and the measurement information.
The present invention has been made in view of the above circumstances, and provides a tire pressure monitoring system. More specifically, the invention provides the tire pressure monitoring system which is able to determine positions of all tire-based transmitting and receiving devices while performing request transmitting processing of transmission requests and information receiving process of identification and measurement information.